The present invention relates generally to agricultural harvesting machines and more specifically to apparatus for detecting the presence of foreign objects, such as stones, within the crop material processed by these harvesters.
Generally forage harvesters include a crop harvesting header mounted at the forward end thereof to initiate the crop harvesting process. The header consolidates the harvested crop and presents it to a centrally located feed mechanism comprising of one or more pairs of parallel and opposing, counter-rotating rolls such as feed rolls and conditioning rolls.
The paired feed rolls form the crop into a mat by forcing it into the space, or nip, between the rolls and then compresses the crop. Generally one roll, of the pair of feed rolls, displaces relative to the other in response to changing crop density and thereby passively adjusts the spacing of the nip; the displaceable roll being held in opposition to the stationary roll by springs, coils or similar mechanisms.
The mat of crop is then delivered across a shear bar where it is cut into short lengths by the blades of a rotating cutting drum. The cutting drum rotates past the shear bar at speeds of 1000-1200 revolutions per minute or more. Typically, feed roll speed can be adjusted depending on the crop conditions and the desired chop length, with faster feed roll speeds resulting in a longer chop length.
To avoid damage, it has been an objective to eliminate foreign matter from the flow of harvested crop before it reaches the rotating cutting drum. Foreign matter includes stones, wood and other debris which can damage the cutting drum or the blades mounted on the cutting drum. The cost of repairing a damaged cutting drum can be in the tens of thousands of dollars and result in significant down time. Furthermore, if any of the blades are dislodged by the impact with the foreign matter, these blades can be thrown into the upstream parts of the harvester, such as the accelerator/blower, and create even more damage. Therefore, it is desirable to be able to sense the presence of foreign objects in the crop material passing through the harvesting machine, and stop the transport of the crop material when a foreign object is sensed, thereby preventing the foreign object from reaching the cutting drum.
The presence of foreign objects in harvested crop material has long been recognized as a problem. Generally speaking, two types of foreign object detectors are known in the art. One type, generally referred to as metal detectors, detects ferrous objects and stops the crop feed mechanism upon detection of such an object. U.S. Pat. No. 4,433,528 to Bohman discloses such a metal detector mounted in a hollow feed roll which includes a magnetically sensitive system to detect the presence of ferrous material in the crop.
A problem addressed by these metal detection devices is where the crop is destined for use as an animal feed and the subsequent ingestion of metal by animals results in a condition known as xe2x80x9chardware diseasexe2x80x9d. Often the metal material detected is stray fencing wire or fencing staples which are no direct threat to the cutting drum and are simply processed along with the rest of the crop. Larger metal pieces, such as tools dropped by accident on the field, would cause damage to the cutting drum, and hence these metal detectors do provide a limited form of protection against such damage.
One major disadvantage of such a detection system is that many foreign objects are non-ferrous, including rocks and wood pieces, and thus are not detected. This is not surprising as these detectors were designed to address the xe2x80x9chardware diseasexe2x80x9d problem rather than to prevent damage to the cutting drum. Overall, however, rocks are a much more common occurrence in the field than are stray metal pieces.
A second type of detector, generally referred to as a stone detector, detects stones and other hard objects including metal objects. Stone detectors may take many forms and be located at various positions in the harvesting machine. For example, in U.S. Pat. No. 3,990,218 to Graeber a pressure-sensitive switch, attached in parallel behind the sickle bar of the harvester""s header, senses rocks and other foreign objects by virtue of their greater relative weight compared to that of the crop material.
The primary disadvantage of this detection device is that it would only work on a harvesting machine in which the header comprises a cutting device, such as a sickle or cutter bar. However, most forage harvesters operate using a pick-up to gather previously severed crop, because efficiencies can be realized by using a separate swather machine to cut the crop quickly and then harvesting the cut swath with a forage harvester. Hence a forage harvester with a pick-up header is unable to use such a device because it lacks a sickle bar. Furthermore, the relative weight of foreign objects such as wood pieces may not be sufficient to trigger the pressure-sensitive switch and such foreign objects may also be bounced or thrown over top of the pressure sensitive switch depending on how they impact the sickle bar.
A more common form of stone detector is an acoustically activated detector. For instance, U.S. Pat. No. 4,353,199 by Chow et al., discloses a detector mounted inside a hollow feed roll. The detector in this device senses acoustical vibrations set up in the feed roll as a result of the impact of hard objects on the feed roll. These acoustically triggered systems are theoretically capable of detecting both ferrous and non-ferrous foreign objects, but have the severe limitation in that foreign objects are often embedded within the crop mat and therefore create insufficient noise to trigger the system as they pass through the harvester. Furthermore, these types of detectors can not be easily retrofitted into forage harvesters because they require the disassembly of the feed roll mechanism and are complex in design.
Even combining a metal detector with an acoustic detector in the same feed roll, as in U.S. Pat. No. 5,092,818 to Bohman et al., does not provide any particular advantage as embedded, non-ferrous, foreign objects do not trigger either of these types of detectors.
Ideally, a device designed to detect foreign objects in crop material would be able to detect a wide range of foreign object types, including those embedded inside the crop material, be capable of functioning on a range of forage harvesters including those with pick-up units, and be easily retrofitted into those harvesters without an existing foreign object detector.
The foreign object detector of the present invention includes an inertial sensor mounted in the feed mechanism of a forage harvester and additional circuitry so as to shut down the feed mechanism if a foreign object is detected. The feed mechanism of a harvester typically comprises a pair of parallel counter-rotating feed rolls which compress the crop into a mat by forcing it into the space, or nip, between the rolls. Generally one roll, of the pair of feed rolls, is displaceable relative to the other in response to changing crop density and thereby passively adjusts the spacing of the nip; the displaceable roll being held in opposition to the stationary roll by springs, coils or similar biasing mechanisms.
The detector""s inertial sensor is mounted for displacement with at least one of the rolls of a pair of counter-rotating parallel feed rolls in the feed mechanism of a forage harvester. The sensor is capable of sensing acceleration. When the sensor""s acceleration exceeds a predetermined threshold, a signal is generated or emitted which causes the feed mechanism to stop. Preferably the sensor is a switch with an inertially-actuated lever, or the sensor is an accelerometer coupled with circuitry to compare the sensed acceleration against a predetermined acceleration threshold.
Should a rock, or other substantially non-compressible object, embedded in the normally compressible crop mat, be forced through the rolls the displaceable roll will experience a rapid displacement relative to its previous position and hence undergo a much greater acceleration than that experienced during normal operations. Such an acceleration exceeds the predetermined threshold, signaling the detector to stop the feed mechanism.
In one embodiment, the detector comprises a microswitch sensor and additional circuitry. The microswitch sensor is mounted for displacement with the upper, displaceable, feed roll. The additional circuitry ties into existing metal detector circuitry, in series, so that either objects or metal can trigger the circuit to stop the feed mechanism. When a foreign object causes the upper feed roll to quickly accelerate upward, the microswitch sensor is tripped and the additional circuitry interrupts the sensing wire of the metal detector, thereby simulating the presence of a metal object, and signaling the metal detector to stop the feed mechanism.